Paper products generally in the form of a cellulosic web, such as paper towels, wipers, and facial tissue are manufactured widely in the paper making industry. Each product has unique product characteristics requiring the appropriate blend of product attributes to ensure that a product can be used in its intended use locus. These attributes include tensile strength, water absorbency, softness, and bulk.
To achieve these product attributes, different manufacturing processes are utilized. One common process is embossing. Embossing increases the bulk of the product and enhances absorbency. In addition, embossing improves the product's aesthetic appeal. Generally, a stiffer web is easier to emboss because the more resilient the web is, the more difficult it is to retain the embossing pattern. However, increasing web stiffness has an adverse impact on web softness. Also, traditional embossing methods reduce the strength of the web. Therefore conventional embossing techniques tend to reduce the strength of the web in an effort to attain suitable bulk.
Conventional embossing techniques include a matched pair of embossing rolls, arranged to move relative to each other to form a roll nip. Generally the web is embossed by passing it through matching male and female embossing elements. The protrusion of the male element on one roll matches within the depression of the female element on the opposite roll, thereby deflecting the web and imparting an embossment at that point. The amount of penetration by the male element into the female element affects the extent of embossing. Traditional embossing techniques have been concerned with varying the amount of penetration. Embossing patterns have been altered in order to increase bulk yet maintain web strength. Much of these conventional embossing improvements have centered on the configuration of the embossing pattern. For example, the embossing pattern has been altered to produce a higher bulk and softer embossed sheet. See U.S. Pat. No. 5,562,805 to Kamps et al., where fine-scale intermeshed embossing elements of two rolls emboss the tissue thereby increasing tissue surface fuzziness which can improve softness.
Recent attempts have concentrated on the distinct geometry of the male and female embossing elements. For example, U.S. Pat. No. 5,356,364 to Veith et al. utilizes unmatched male and female embossing elements. The side wall slope of the matched elements are different, causing the web to be pinched at distinct points within each embossing element.
Other recent improvements in embossing methods involve adding a ridge or shoulder to the embossing elements. See U.S. Pat. No. 4,543,142 to Kuepper et al, where a shoulder is placed at the elements mid-plane. See also, U.S. Pat. No. 4,921,034 to Burgess et al, where a paper product has a plurality of bosses alternating about a centered shoulder.
Other attempts to improve the embossing pattern have involved changing the roll material from traditional steel to a softer material. See U.S. Pat. No. 4,211,743 to Nauta et al., where the embossing rolls have a resilient surface of varying hardness. The resilient surfaces temporarily deform within the nip thereby ensuring that the web material is fully contacted by the embossing pattern.
Traditional embossing methods of cellulosic webs continue to have many shortcomings. There is a need for an embossing method that increases the bulk of the web while maintaining adequate web strength.